1. Field of the Invention
The invention relates to tube joints. It concerns in particular joints for tubes having a small diameter and/or a thin wall, such as are used for distributing fuel in aircraft or automobile engines.
2. Discussion of Prior Art
Generally, for the purpose of forming such a joint, the outer end of the tube to be joined is first provided with a cylindrical sleeve which can be anchored on said end, after which the sleeve is pressed into a joint member with a nut which is screwed on to the latter. It is essential that the anchoring of the sleeve on the tube should not cause the formation of lines or zones of reduced strength, particularly if the tube is of small wall-thickness. The process that seems to have met these technical anchoring requirements the most satisfactorily comprises the expansion of the end of the tube within the sleeve. The expansion process is very old and consists in introducing, into the tube, a mandrel of variable diameter so as to cause radial internal pressure which urges the tube against the inner wall of the sleeve which is provided with ribs and channels. In this method, an axially compressible mandrel is introduced into the tube, and then, with the help of a suitable system, the circumference of the mandrel is caused to expand in the zone of the channels in the sleeve, and the wall of the tube is thus radially pressed towards the bottoms of said channels. Then, after this interior shaping of the tube has been completed, the compression force is relaxed and the mandrel is withdrawn. The tube remains anchored in its sleeve and can then be connected in the usual manner by means of a joint member and a nut which can be screwed on to it.
The sleeves or sockets most frequently used are relatively long and for the purpose of achieving adequate anchoring, they comprise two spaced channels defining a separating rib and an end rib. Since the extent to which the tube cna be deformed is limited, the presence of a plurality of ribs in the sleeve is necessary to ensure an adequate latching action.
Although this process has been generally satisfactory, it involves difficulties and has been found inadequate for reliably meeting technical requirements that are becoming progressively more stringent. In the first place, the compressible mandrel is fragile and breaks when used in tubes of small diameter, and the process is increasingly more difficult to use as the wall-thickness of the tube diminishes. In the zone of the ribs and channels of the sleeve, and consequently in the zone where the diameter is expanded, the tube is stretched radially and longitudinally, and the thickness of its wall therefore diminishes slightly, and this is noticeable in a tube having a very thin wall. The presence of the ribs causes folding of the material of the tube accompanied by the onset of lines of reduced strength which are aggravated when the sleeve is pressed into the joint member and into the clamping nut. Furthermore, due to the presence of two channels, the conventional excess thickness of a sleeve corresponds only to the central channel, and a thin zone corresponds to the other channel or channels.
To overcome these difficulties, the Inventor has developed an anchoring process of the type consisting in deforming a tube within a sleeve having an interior channel, which process is characterized in that the deformation of the tube is achieved by the application of pressure to the end portion of its wall, a solid rigid mandrel having a smooth wall being temporarily placed within the tube, and preventing any inward deformation, and the pressure applied longitudinally at the end ofsuch tube causing deformation by upsetting of the wall of the tube in the zone of the channel in the sleeve, in such manner that the sleeve and the tube are undetachably secured to each other.
To achieve deformation only in the zone of the channel or channels in the sleeve, the tube and optionally its sleeve, as well, are held in position on the outside by one or more sockets and/or shells, and on the inside by a mandrel of suitable diameter, so that the only zone of expansion is determined by the channel in the sleeve. In one embodiment of the method, the mandrel is introduced into the tube and at the same time pressure is applied to the end portion of the tube on completion of the stroke of the mandrel. For this purpose, the mandrel comprises a suitable shoulder for moving into abutment with the end portion of the tube and then applying pressure thereto. In another embodiment, the tube extends slightly beyond the sleeve, and the mandrel comprises two spaced shoulders so that when it is introduced into the tube, the first shoulder causes the tube to expand, and the second shoulder applies pressure to the end portion of the tube. In a still further embodiment of the invention, two mandrels are used in succession. The first mandrel comprises a single shoulder which is applied to the end section of the tube and serves only to apply the pressure necessary for effecting deformation in the zone of the channel or channels in the sleeve. During this operation, the portion of the tube that extends beyond the sleeve is held in position by a suitable socket. After the first mandrel has been retracted, a second mandrel having a single shoulder and a wider portion is introduced into the tube so as to expand the portion extending beyond the sleeve and to apply the deformed portion to the end of said sleeve.
The invention covers not only the process,but the joint too. The sleeve used comprises a cylindrical bore without any internal ribs or other projections, but having a wide channel located at an externally thickened portion, preferably provided approximately midway along its length. Advantageously, the sleeve comprises a second channel within the first channel. This second channel is of smaller width, but has a greater diameter than that of the first channel. The second channel may be formed at any place in the bottom of the first channel, for example, along one edge of the first channel or at the middle thereof in such a way that a circular area of said first channel is present at each side of the second channel, thus defining the necessary anchoring and sealing shoulders. Where, in accordance with the process, the wall of the tube is seated in a sleeve having one channel, said wall has two circular attachment zones corresponding to the two shoulders defined by the channel within the sleeve. Where the wall of the tube is seated in a sleeve having a plurality of concentric channels, the wall of the tube comprises three or four circular attachment zones corresponding to the two or three shoulders defined by the two circular channels within the sleeve; the number of shoulders being dependent upon whether the second channel is or is not located at an end of the first channel. The expanded portion of the tube extends beyond the sleeve and the zone of deformation interconnecting the expanded and non-expanded portions is applied to the end of said sleeve, and this constitutes an additional shoulder and therefore an additional circular attachment zone.
After the end of the tube has been deformed, the mandrel and the sockets are withdrawn and the tube, seated in its sleeve, can then be connected with the aid of a joint member and of the nut screwed on to it.